After the failed Northern Rebellion of 1569, Thomas Howard, 4th Duke of Norfolk was kept a
virtual prisoner, under house arrest at Howard House. He retired from public life and many of his
roles and responsibilities as the leading peer in England were deputised to others.

Early in 1571 Mary began to seek a solution to her problems outside England. Roberto Ridolfi, an
energetic and imaginative Florentine banker, who had already been in Walsingham's custody for his
implication in the events of 1569, acted as papal agent and intermediary between Mary, her agent,
the bishop of Ross, her English supporters, and Spain. An extensive, overmanned, and vulnerable
conspiratorial network, including the servants of the principal participants, planned the release of
the Scottish queen, her marriage to the duke, and, with Spanish military assistance, Elizabeth's
removal in favour of Mary and the restoration of Catholicism in England. The success of the plan
required Norfolk's approval and involvement. An initial approach by the bishop of Ross, forwarding
ciphered letters from Mary, failed to secure his support. However, Norfolk reluctantly agreed to
meet Ridolfi, as a result of which he gave verbal approval to the request for Spanish military
assistance. His name was also subscribed to letters to the pope, Philip II, and the duke of Alva,
Philip's commander in the Netherlands.

The Ridolfi plot was exposed more as a result of a series of accidents than of deliberate
official investigation. Servants of Mary's agent, the bishop of Ross, and of Norfolk did not prove
adept at avoiding suspicion and detection as they travelled with ciphered letters and money for
their supporters. On about 12 April 1571 Charles Bailly, Ross's servant, was caught with letters for
him at Dover. Then, on 29 August, Norfolk's secretaries William Barker and Robert Higford entrusted
to Thomas Browne, a Shrewsbury draper, what purported to be a bag of silver coin for delivery to
Laurence Bannister, one of the duke's officials in the north of England. Browne grew suspicious of
the bag's weight, opened it, and discovered £600 in gold from the French ambassador and destined for
Scotland on Mary's behalf. It also contained ciphered letters. Because he knew that Norfolk was
under suspicion Browne reported his find to Cecil, now Lord Burghley. Higford and Barker were
examined, the letters were partly deciphered, and a search for the cipher key at Howard House
uncovered a ciphered letter from Mary Stuart hidden under a doormat. From this point the duke's
failure to honour his submission was revealed and his complicity in a wider treasonable conspiracy
was established.

Norfolk's servants were arrested and interrogated and confessions were extracted from them by
threats or application of torture. Sir Thomas Smith and Thomas Wilson were sent to confront Norfolk,
who claimed that the £600 was for his own private purposes. The deciphered letter, however, proved
that he was lying. Unaware of his servants' confessions or the survival of letters which, contrary
to his instructions, had not been burnt, he denied the charges against him. On 7 September the
queen's warrant for conveying him to the Tower arrived. Thereupon the duke admitted a degree of
involvement in the transmission of money and correspondence to Mary's Scottish supporters, before
he was taken through London to the Tower. A servant of the Spanish ambassador reported that those
who witnessed this were vocal in Norfolk's favour. Guerau de Spes, the ambassador, referred to
‘this popularity of his amongst the common people’. He observed that ‘the concourse of people was
so large and the shouts so general that a very little more and he would have been liberated’ (CSP
Spain, 1509–25, 335).

In the following weeks the duke and his servants were subjected to repeated examinations which,
together with his confessions, confirmed his disloyalty to Elizabeth, the breach of his own
submission to her, and his complicity in conspiracy. In January 1572 he was tried and convicted on
three counts of high treason, and on 2nd June he was beheaded on Tower Hill.

By now it was becoming clear to Elizabeth's supporters and the nobles that formed her inner circle that
Mary had become the focus of conspiracy and was seen as the Catholic figurehead in any attempt at
rebellion against the crown.